The present study was undertaken to investigate the effects of ${eta}-eudesmol$, one of various ingredients isolated and identified from the bark of Magnolia obovata Thunberg, on arterial blood pressure and vascular contractile responses in the normotensve rats and to establish its mechanism of action. ${eta}-Eudesmol;(30{sim}300;{mu}g/kg)$ given into a femoral vein of the normotensive rat produced a dose-dependent depressor response. These ${eta}-eudesmol-induced$ hypotensive responses were markedly inhibited in the presence of chlorisondamine (1.0 mg/kg, i.v.) or phentolamine (2.0 mg/kg, i.v.). Interestingly, the infusion of ${eta}-eudesmol$ (1.0 mg/kg/30min) into a femoral vein made a significant reduction in pressor responses induced by intravenous norepinephrine. Furthermore, the phenylephrine $(10^{-5};M)-induced$ contractile responses were depressed in the presence of high concentrations of ${eta}-eudesmol;(10{sim}40;{mu}g/ml)$, but not affected in low concentration of ${eta}-eudesmol;(2.5{sim}5;{mu}g/ml)$. Also, high potassium $(5.6{ imes}10^{-2};M)-induced$ contractile responses were greatly inhibited in the presence of ${eta}-eudesmol;(10{sim}40;{mu}g/ml)$ in a dose-dependent fashion. Taken together, these results obtained from the present study demonstrate that intravenous ${eta}-eudesmol$ causes a dose-dependent depressor action in the anesthetized rat at least partly through the blockade of vascular adrenergic ${alpha}_1-receptors$, in addition to the some unknown mechanism of direct vasorelaxation.